Investigation of the localized surface plasmon effect from Au nanoparticles in ZnO nanorods for enhancing the performance of polymer solar cells.

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Nanoscale View Article Online

DOI: 10.1039/C4NR05194G

Investigation of Localized Surface Plasmon Effect from Au Nanoparticles in ZnO Nanorods for Enhancing Performance of Polymer Solar Cells

and Ching-Fuh Lin*a,b,c a

Graduate Institute of Photonics and Optoelectronics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, ROC.

b

Graduate Institute of Electronics Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, ROC. c

*

Department of Electrical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, ROC.

Corresponding author. Address: Institute of Photonics and Optoelectronics, National

Taiwan University, Taipei, 10617 Taiwan, Republic of China. Tel: +886-2-33663540; Fax: +886-2-23642603. E-mail address: [email protected]

Abstract The organic polymer solar cell is recognized as one of the most competitive technologies in the next generation. Here we combine Au nanoparticles and ZnO nanorods to improve the inverted-structure low-bandgap polymer solar cells through enhancing the absorption and efficiency of the devices. However, the experiment shows that the Au nanoparticles tend to aggregate in the solution, thus reducing the localized surface plasmon resonance (LSPR) effect. The cluster effect on the spectral range of enhancement in the absorption is investigated and the absorption characteristics of the LSPR receive proper modification through our experiment. With the reduced Au nanoparticle clusters, the experiment clearly verifies the LSPR effect in the devices. The proper combination of the Au nanoparticles and ZnO nanorods leads to the power conversion efficiency of the

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Published on 10 November 2014. Downloaded by UTSA Libraries on 15/11/2014 12:53:21.

Yu-Che Ho,a Shao-Hsuan Kaoa, Hsin-Che Lee,a Sheng-Kai Chang,a Cheng-Che Lee,a

Nanoscale

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DOI: 10.1039/C4NR05194G

PTB7:PC71BM inverted organic solar cell reaching 8.04% after optimizing the processes conditions.

Over the past few years, organic solar cells have been regarded as the most prospective source of green energy in the future by taking its advantages of flexibility and potential to achieve large-scale and low-cost manufacturing under the solution process.

1-3

.

The efficiency and the life time of polymer organic cells are influenced by the absorptivity and stability of the device structure and material. The inverted-structure organic solar cell adopts high work function metal as the anode and avoids PEDOT:PPS on ITO.4, 5 It helps reduce the negative effects to the structure and life time, thus enhancing the efficiency and stability of the device.6-16 Cs2CO3 17, 18, TiOx

19, 20

, and ZnO

21, 22

are three kinds of electron

extraction layer that have been published in the articles to modify ITO. The features of ZnO are that it has a wide energy gap, the capability to match with the energy level of the polymer active layer, and the potential to allow large-scale solution process.23 In earlier articles, there were discussions about different processes for generating a ZnO layer.24, 25 Also, the method of growing ZnO nanorods via a hydrothermal process was used for penetrating into the active layer to extract carriers so that it could improve the short mobility distance of the organic material carrier and insufficient absorption caused by the lack of thickness on the device. To further enhance the device performance, we adopt localized surface plasmon resonance (LSPR) effect and apply it with the ZnO nanorod arrays in the inverted-structure organic cell. The metal nanoparticles, Au in this study, are blended into the organic active material. With the organic active material flowing into the spacing of the ZnO nanorod arrays, the 4 nm Au nanoparticles can exist in the spacing of the ZnO nanorods. Because the free vibration electron on metallic surfaces interacts with the photons from external

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1. Introduction

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interference, plasmon oscillation occurs and begins to transport dilatational waves along the metallic surface.26 Moreover, due to the uncertainty principle, the matching criteria of light energy and momentum are easy to meet after the space is localized. This brings out an

surface, which is called localized surface plasmon resonance.27 In other words, through the application of surface plasmon resonance, the additional absorption (in particular the wave band) of the organic active layer material is therefore increased. In past studies, it was confirmed that adding metallic nanoparticles onto polymer solar cells or establishing ordered metallic nanostructure were effective for boosting the light absorption and the potential of photocurrent, thereby enhancing the photoelectric conversion efficiency.28-30 Currently, there are applications that employ metallic nanoparticle surface plasmon resonance onto the conventional structure of the device

31-36

, the tandem polymer solar cells

37, 38

, and the

devices with nanorod structures and metallic nanoparticle sputtered on.39, 40 For LSPR, the size of nanoparticles has to be smaller than a certain number, such as smaller than 25 nm, to effectively excite the LSPR.41 In addition, the absorption spectrum due to LSPR depends on the size of metallic nanoparticles.41-43 However, past studies using metallic nanoparticles for polymer solar cells have not clearly indicated that the size of the added metallic nanoparticles well matches the mechanism of LSPR.34 Therefore, it was impossible to distinguish exactly if the enhancement was prompted by the LSPR or the scattering effect. The aggregation would alter the main mechanism of metallic nanoparticles from the LSPR effect to the common scattering effect.43 From the experiment, we discovered that once the process was not kept in a low temperature environment, the Au nanoparticles in the solution would bring about intense clustering and affect their absorption spectrum performance on the LSPR effect. After the clustering, Au nanoparticles had a tendency to act as an enlarged effective size, so a red shift

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obvious enhanced electromagnetic resonance effect from the near field of the nanoparticle

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appeared on the absorption spectrum. However, the result didn’t seem to be observed as the expected performance from the actual Au nanoparticles size. In fact, the red shift on the absorption-enhanced band gave the device worse absorption performance. As a result, we

performance of a device, we used the pretreatment of ultrasonic vibration to break apart the clustering of Au and obtain the feature of absorption spectrum that matched the LSPR effect of the correct Au nanoparticles size. From above, we also verified that it was the surface plasmon effect giving to the enhancement of absorption. Through adjusting the morphology, concentration, and doping method of Au nanoparticles, we were able to excite the surface plasmon effect of metallic nanoparticles by evenly doping the appropriate small-sized Au nanoparticles into the organic active material. We then applied the optimized morphology of ZnO nanorods with a longer length. Because of more volume of the rod spacing for active material to fill in, the effective thickness for light absorption is increased. Also, the ZnO nanorods that were embedded into the active layer can serve as a carrier pathway and help the carrier transport. Furthermore, the nanorod morphology of ZnO provided an amelioration of increasing the interface contact between organic and inorganic materials. Therefore, the optimization increased the absorption of the organic active layer, enhanced the transport and collection of carriers, and improved the absorption of light.44, 45 In order to achieve the best performance, the thickness of MoOx hole transport layer which could influence the short-circuit current and fill factor was fine-tuned.45 As a result, under single junction configurations, the development of an inverted-structure organic cell was encouraged to pursue higher efficiency performance. By employing the doping of small-sized Au nanoparticles to induce the surface plasmon effect and embedding a ZnO nanorod array in the organic active material, the PTB7: PC71BM inverted organic solar cell system reached 8.04% photoelectric conversion efficiency.

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discuss in the following on the solution we devised. In order to get the best absorption

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2. Experiment The devices were fabricated in an inverted structure. The active layer PTB7/PC71BM was sandwiched between MoOx (molybdenum oxide) and ZnO, with ITO and Ag employed

In order to embed a ZnO nanorod array in the organic active material, a seed layer coating process and a hydrothermal growth process were used. Firstly, the sol-gel ZnO seed layer was prepared by mixing zinc acetate dehydrate (Zn(CH3COO)¬22H2O Sigma-Aldrich, ≥99.0%) in 2-methoxyethanol (CH3OCH2CH2OH) (Alfa Aesar, 99%) and ethanolamine (NH2CH2CH2OH). Secondly, the sol-gel was spin-coated on the cleaned ITO-coated glass substrate to form a ZnO seed layer. Afterwards, the device was annealed at 200℃ for an hour in nitrogen. In the next step, to fabricate the ZnO nanorod array, a growth-promoting solution for the hydrothermal process was prepared with zinc nitrate, HMT, and DI water. The hydrothermal process was implemented at 90℃ for 80 minutes, with the device suspended in the solution upside down. As the hydrothermal process finished, the device with the wellgrown ZnO nanorod array was cleaned by IPA and DI water. Next, to prepare the active layer material, PTB7/PC71BM (with a weight ratio of 1:1.5) was dissolved in 1,2-dichlorobenzene/chlorobenzene mixed solvent (with a volume ratio of 1:1) with a 3% additive solvent of 1,8-Diiodooctane (DIO). In order to fabricate the solar cell devices with LSPR, 4 nm Au nanoparticles were then blended into the active layer material. Moreover, after Au nanoparticles were blended, ultrasonic vibration pretreatment with different period of time (from 0 to 60 minutes) was adopted to reduce the aggregation of Au nanoparticles. Then the active layer material was spin-coated on the surface of the ZnO nanorod array in the glove box. A subsequent post-treatment of 5 hours dried in the glove box was applied.

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as electrodes.

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Lastly, after the active layer being implemented, the devices were fabricated with molybdenum oxide (MoOx) deposited using thermal evaporation as the hole-transport layer and silver (~250 nm) as the back contact through thermal evaporation in a 3×10-6 Torr

2400 source meter under solar irradiation, simulated by a SUN 2000 (Abet Technologies, Inc.). The solar illumination, generated by a Thermo Oriel 150 W solar simulator with AM 1.5G filters, was calibrated at the intensity of 100 mW/cm2 by a NREL certificated monocrystalline silicon reference cell (PVM-236). The incident photon conversion efficiency (IPCE) was measured, using QE-R-3015 (Enli Technology Co., Ltd.). The lamp was calibrated using a mono-crystalline silicon reference cell provided by Newport Corporation.

3. Results and Discussion In the inverted-structure polymer solar cell, it is not easy to keep the high FF and level of the absorption and the photocurrent solely through alternating the concentration and thickness of the active layer. Hence, by combining ZnO nanorods and the surface plasmon effect of Au nanoparticles, Au nanoparticles can enhance the absorption. Also, the generated carriers that have been separated by the additional exciton can transport through the channel provided by ZnO nanorods. In this way, it helps the absorption of the active layer and makes even more effective use of solar light. Besides, in the past studies, we have proven and also applied ZnO nanorods to enhance the efficiency of the inverted polymer solar cell.

46-52

As a

result, the ZnO nanorods, which were 90 nm in average height, 27 nm in average spacing and 25 nm in diameter was used as the electron transport channel.53 The SEM images of ZnO nanorods and the active layer are shown in Figure 1. The thickness of the active layer was 160 nm. The devices with Au particles shown in Figure 1 (c) and Figure 1(d) had been pretreated with ultrasonic vibration. From the SEM images, the 20 nm Au can be observed.

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vacuum. The current density-voltage (J-V) characteristics were measured with a Keithley

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They appear as bright spots above the nanorods in the SEM image. However, the 4 nm Au particles embedded inside the active layer cannot be observed because they were too small. We added Au nanoparticles into the active layer of the device, which was embedded

band diagram is showed in Figure 2(b). The size of Au nanoparticles is important. First, it has to be small enough to be embedded into the spacing among ZnO nanorods. Second, the size should well correspond to the absorption spectrum of PTB7/PC71BM blend so that the LSPR can be induced to enhance the solar-cell performance. In order to make an effective arrangement of morphology of ZnO nanorods and Au nanoparticles, we inferred from Figure 1, SEM images of ZnO nanorods, that if the Au nanoparticles were not chosen in appropriate size, they would stick on the top of the ZnO nanorod array and cause difficulty on the permeating of the active layer material. Therefore, the 4nm Au nanoparticles were adopted to apply in the active layer for coordinating with the ZnO nanorod spacing, ranging from less than 10 nm to over 40 nm, although the average was 20-30 nm. The method was to observe how the different Au nanoparticle concentrations influenced the absorption and efficiency performance of the solar cell. By adding different concentrations of Au nanoparticles, the increase of the device’s absorption spectrum band and absorption amount can be seen in Figure 3. From the observation of the absorption spectrum, we knew that the surface plasmon resonance of Au nanoparticles contributed a considerable degree of absorption on the organic active layer. In addition, when the concentration increased, the spectrum showed the absorption values rose around the range from 550 nm to 700 nm. The characteristic peak was located at 610 nm. Due to the increase of the active layer absorption, the amount of carriers increased, and the JSC of the device therefore increased as well.

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with ZnO nanorods. The illustration of the device is shown in Figure 2(a), and the energy

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However, according to Figure 4, the optical analysis of 4 nm Au nanoparticles size from nanoComposix Company, the localized surface plasmon of a 4 nm particle should correspond to around 500 nm absorption band, theoretically speaking. In comparison with the

match the localized surface plasmon effect of this nanoparticle size. Yet, at the same time, the absorption band, which was contributed by a localized surface plasmon effect, would theoretically move toward higher wavelengths as the particle size increased.30, 41 Therefore, we inferred that the use and the preservation of 4 nm Au nanoparticles would affect its dispersion. If the dispersion was in poor circumstances, then it would cause a cluster and show an absorption tendency that is similar to the large particle size. Figure 5 shows the atomic force microscopy (AFM) phase image analysis of the cluster and distribution condition with Au nanoparticles in the active layer. For the scan range of 500 nm x 500 nm, we observed a lot of clusters that were composed of many small dots. From the AFM, some small dots are under 10 nm and the size of the clusters ranges from 50 to 100 nm. The above confirms the distribution of the nanoparticles in the active layer: because of the selection of solution, the preservation method, and the stirring, the nanoparticles were not ideally distributed evenly, but rather unevenly clustered into small pieces. This phenomenon was attributed to the condition that the colloidal solution of Au nanoparticles was in an imbalanced state of thermodynamics, so the ambient temperature was likely to have a drastic impact on the preservation of the colloidal solution of Au nanoparticles. However, when preparing the active layer, the nanoparticles must separate from the low temperature and light-protected environment. Furthermore, it needed to go over the heating and stirring process so that the high temperature at this point would induce cluster and precipitation of the nanoparticles in the solution.

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absorption measurements in Figure 3, the red shift of the increased absorption area did not

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To further confirm that the cluster of Au nanoparticles had an impact on the shifts of absorption-enhanced wave band, and to prove the device enhancement was led by a localized surface plasmon effect, the solution was therefore prepared ahead. The solution adopted

nanoparticles and to improve its homodispersion. In the experiment prior to spin coat, we ultrasonically treated the active layer solution that contained 0.20mg/mL Au nanoparticles from 0 to 60 minutes. The method precipitated the cluster of Au nanoparticles, so the actual distribution of nanoparticles gradually became ideal. After fabricating the device, the measurement of absorption spectrum is exhibited in Figure 6. The measurement of the device efficiency performance is shown in Table 1 and its J-V curve is displayed in Figure 7. According to the absorption spectrum, as the processing time of ultrasonic vibration was increased, the absorption spectrum between 450 nm and 570 nm began to enhance. In the meantime, the absorption-enhanced characteristics above 600 nm started to decline after the treatment. The decline could be obviously observed soon after 1 or 2 minutes of treatment. As the process time of ultrasonic treatment prolonged to 60 minutes, the characteristic peak of the surface plasmon effect came near to 510 nm. On the contrary, the wave band where the absorption enhanced before going through the ultrasonic pretreatment now shared the same characteristics with the device that didn’t add Au nanoparticles. Due to the fact that the Au nanoparticles started improving their dispersibility all over again, it reduced the chances of the cluster of lager-sized metallic nanoparticles. As a result, the surface plasmon effect of 4 nm Au nanoparticles was enhanced at 510 nm. Therefore, through adjusting different concentrations of Au nanoparticles and then going through an ultrasonic vibration pretreatment process for 60 minutes, the devices that have been fabricated accordingly showed their absorption spectrum in Figure 8. Compared with Figure 4, the enhanced peak of this spectrum shows good correspondence to the absorption

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pretreatment of ultrasonic vibration to break apart aggregation or precipitation of Au

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characteristic of the metallic surface plasmon effect. It also shows that once the concentration increases, the absorption near the 510 nm band also enhances. While the concentration increases, the peak in the absorption shows an enhancement but without significant shift.

concentrations all appear between 450 nm and 570 nm. On the other hand, the LSPR effect is enhanced when there are more Au nanoparticles, so the peak increases with the concentration. In brief, in this series of experiments, we found that the application and pretreatment of metallic nanoparticles have an impact on the performance of the device. Meanwhile, by comparing the characteristics of the absorption before and after the treatment, we verified that the surface plasmon effect of metallic nanoparticles played the leading role on the device’s absorption enhancement. Table 1 demonstrates the device performance from different concentrations of Au nanoparticles. In comparison with the device without Au nanoparticles, the one with Au nanoparticles enhanced the Jsc due to the fact that the Au nanoparticle surface plasmon effect contributed to the absorption enhancement of the active layer. Furthermore, the Jsc kept climbing up as the concentration added up. It reached its peak at 0.20 mg/mL and declined at 0.40 mg/mL. The trend change of fill factor (FF) was similar to Jsc, but FF with Au nanoparticles performed worse than the ones without. FF fell from 65.5% to 65.9% for 0 to 0.20 mg/ml of Au nanoparticles, but it declined to 61.2% at 0.40 mg/mL. The variations here were attributed to Rs and Rsh. The conducting power of Au nanoparticles was far better than conductive organic materials. By adding the right amount of Au nanoparticles, it could also provide a carrier transport shortcut. Therefore, the series resistance of the device dropped as the addition of Au nanoparticles increased. The figure declined from 3.0Ω without Au nanoparticles to 2.7Ω with 0.40mg/mL of Au nanoparticles.

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Because the nanoparticles are dispersed through ultrasonic vibration, the peaks for various

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The addition of Au nanoparticles helped conductivity, yet the electrical conductivity direction was hard to control. Therefore, the leakage of current became severe as the concentration of Au nanoparticles increased. The parallel resistance dropped from 593 Ω

nanoparticles increased. To conclude the above, when the Au nanoparticles concentration was too intense, it generated too many false transport channels, resulting in the loss of carriers. This condition influenced the performance of FF, and the Voc also declined as the concentration increased. As the energy level of Au was set around -5.1~ -5.47 eV (there were slight differences depending on the stacking patterns), it affected the carrier’s ability to separate the built-in electric field on the donor-acceptor material interface. The exceeding addition would damage the material energy match of donor and accepter and caused the decline of Voc. The figure dropped from 0.71 V without Au nanoparticles to 0.65 V with 0.40 mg/mL of Au nanoparticles. The changes of Jsc and FF were decided by the positive and negative sides of the enhancement of device absorption, energy match, and carrier transport. Therefore we tried to maintain the dominance of high absorption and reduce the negative effects of carrier transport. The device increased the effect of its conversion efficiency from 7.22% without Au nanoparticles to 7.55% with 0.20 mg/mL of Au nanoparticles. Even so, in order to achieve the best performance of the device, the thickness of the MoOx hole transport layer required adjustment for strengthening the transporting effect. It is cited that the thinner the active layer, the more sensitive to the thickness of MoOx.45 Also the main factor of the above influences lies upon the short-circuit current and fill factor. Therefore, we took the optimal factor acquired from above to generate the device with diverse thicknesses of MoOx. The parameter of devices is shown in Table 2, and the J-V curve of the device is shown in Figure 9. When using 4 nm MoOx, the external quantum efficiency of the device reached the maximum, as shown in Figure 10, the Jsc enhanced to the

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without Au nanoparticles to 328 Ω with 0.40 mg/mL of Au nanoparticles as the Au

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16.9 mA/cm2, and FF achieved 65.6%. Thus, the best device performance efficiency reached 7.88%. Lastly, the longer ZnO nanorod array was even tried to combine with the Au nanoparticle surface plasmon effect. By replacing the original use of a 90 nm ZnO nanorod

conversion efficiency results and achieved optimal PCE of 8.04%. The performance is shown in Table 3.

4. Conclusion We employed the Au nanoparticles into the active layer of the device and embedded it with a ZnO nanorod array. By adjusting the concentration and the method of doping, we were able to conclude the optimal matching of Au nanoparticles and ZnO nanorod array. Furthermore, the device successfully improved the absorption through the effect of surface plasmon, which is excited by the Au nanoparticles. Also, by the pretreatment of ultrasonic vibration, we effectively reduced the clustering of Au nanoparticles and disturbed the gain band position in the absorption spectrum regarding the surface plasmon effect. From the above results, we confirm that the surface plasmon effect plays a significant role in the absorption of a device. Consequently, the efficiency performance was enhanced from 7.22% to 7.55% through the surface plasmon. Lastly, by optimizing the device through offering a suitable hole transporting layer and an optimal ZnO nanorod array, the polymer solar cell with Au nanoparticles and ZnO nanorod array eventually enhanced the efficiency performance to 8.04% under the single junction configurations.

Acknowledgements This work was supported by the National Science Council, Taiwan, Republic of China, with the project numbers: NSC 100-2923-E-002-005-MY3, NSC101-ET-E-002-001-

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array with 200±10 nm ZnO nanorod array, the enhancement of Jsc brought out higher

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15



Fan, Applied Physics Letters, 2010, 96, 071107.

Nanoscale


DOI: 10.1039/C4NR05194G

Figure Captions Figure 1 The SEM top view (a) and front view (b) of a ZnO nanorod array; and the SEM front view of the active layer with 4 nm (c) and with both 4 nm and 20 nm (d) Au

Figure 2 The structure illustration (a) and the energy band diagram (b) of the polymer solar cell with Au nanoparticles and ZnO nanorod array. Figure 3 The comparison between the absorption spectra of organic active layer devices added, respectively, with 0.10 mg/mL, 0.15mg/mL, 0.20 mg/mL, 0.30 mg/mL, 0.40mg/mL Au nanoparticles, and without. Figure 4 The optical absorption characteristic of the surface plasmon by 4nm Au nanoparticles. This spectrum is provided by nanoComposix Inc. Figure 5 The AFM images of PTB7: PC71BM active layer surface which was added with 0.20 mg/mL Au nanoparticles. Figure 6 The comparison between the absorption spectra of organic active layer devices added with and without Au nanoparticles 0.20 mg/mL via different periods of time of ultrasonic vibration pretreatment. Figure 7 The current-voltage characteristic of the organic active layer devices added with and without Au nanoparticles 0.20 mg/mL via different periods of time of ultrasonic vibration pretreatment. Figure 8 The comparison between the absorption spectra of organic active layer devices added, respectively, with 0.10 mg/mL, 0.15mg/mL, 0.20 mg/mL, 0.30 mg/mL, 0.40mg/mL Au nanoparticles, and without, by ultrasonic vibration pretreatment for an hour. Figure 9 The current-voltage characteristic of the organic solar cells with Au nanoparticles with the evaporation thickness of MoOx hole transport layer is in adjustment. Figure 10 The external quantum efficiency of the organic solar cells with Au nanoparticles with the evaporation thickness of MoOx hole transport layer is in adjustment.

16



nanoparticles.

Page 17 of 29


DOI: 10.1039/C4NR05194G

Table Captions

Table 2 The influence on the device performance by adjusting diverse thicknesses of the MoOx hole transporting layer. Table 3 The device performance of 4 nm Au nanoparticles combined with 200±10 nm ZnO nanorods.

17



Table 1 The performance of PTB7:PC71BM organic solar cell using a ZnO nanorod array by adding different concentration of 4 nm Au nanoparticles.

Nanoscale


DOI: 10.1039/C4NR05194G

Table 1

PCE (%)

Jsc (mA/cm2)

Voc (V)

FF (%)

Rs (Ω/cm2)

Rsh (Ω /cm2)

w/o 4nm Au NPs

7.22

15.2

0.71

66.9

3.0

593

4nm Au NPs 0.10mg/mL

7.35

16.0

0.70

65.6

2.8

610


7.52

16.4

0.70

65.5

2.9

593


7.55

16.6

0.69

65.9

2.7

599


6.73

16.0

0.66

63.7

2.8

500


6.17

15.5

0.65

61.2

2.7

328

Rs (Ω/cm2)

Rsh (Ω /cm2)

Table 2

ZnO nanorod array:PTB7/PC71BM With Au NPs

PCE (%)

Jsc Voc (mA/cm2) (V)

FF (%)

1 nm MoOx as HTL

6.25

14.6

0.71

60.3

3.9

401

2 nm MoOx as HTL

7.17

16.0

0.71

63.1

4.0

501

3 nm MoOx as HTL

7.74

16.8

0.71

64.9

4.0

544

4 nm MoOx as HTL

7.88

16.9

0.71

65.6

4.1

601

5 nm MoOx as HTL

7.54

16.3

0.71

65.1

4.5

596

6 nm MoOx as HTL

7.46

16.2

0.71

64.8

5.0

598

Table 3 ZnO nanorod array:PTB7/PC71BM With Au NPs (Using ZnO nanorod length 200± ±10nm)

PCE (%) 8.04

Jsc Voc (mA/cm2) (V) 17.5

0.71

FF (%) 64.7

Rs (Ω/cm2) 4.0

Rsh (Ω /cm2) 529



ZnO nanorod array:PTB7/PC71BM

Page 19 of 29


Figure 1 The SEM top view (a) and front view (b) of a ZnO nanorod array; and the SEM front view of the active layer with 4 nm (c) and with both 4 nm and 20 nm (d) Au nanoparticles. 99x94mm (150 x 150 DPI)



DOI: 10.1039/C4NR05194G

Nanoscale


Figure 2 The structure illustration (a) and the energy band diagram (b) of the polymer solar cell with Au nanoparticles and ZnO nanorod array. 273x140mm (72 x 72 DPI)



DOI: 10.1039/C4NR05194G

Page 21 of 29


Figure 2 The structure illustration (a) and the energy band diagram (b) of the polymer solar cell with Au nanoparticles and ZnO nanorod array. 184x140mm (72 x 72 DPI)



DOI: 10.1039/C4NR05194G

Nanoscale


Figure 3 The comparison between the absorption spectra of organic active layer devices added, respectively, with 0.10 mg/mL, 0.15mg/mL, 0.20 mg/mL, 0.30 mg/mL, 0.40mg/mL Au nanoparticles, and without. 112x85mm (209 x 209 DPI)



DOI: 10.1039/C4NR05194G

Page 23 of 29


Figure 4 The optical absorption characteristic of the surface plasmon by 4nm Au nanoparticles. This spectrum is provided by nanoComposix Inc. 357x273mm (72 x 72 DPI)



DOI: 10.1039/C4NR05194G

Nanoscale


Figure 5 The AFM images of PTB7: PC71BM active layer surface which was added with 0.20 mg/mL Au nanoparticles. 74x55mm (168 x 168 DPI)



DOI: 10.1039/C4NR05194G

Page 25 of 29


Figure 6 The comparison between the absorption spectra of organic active layer devices added with and without Au nanoparticles 0.20 mg/mL via different periods of time of ultrasonic vibration pretreatment. 120x90mm (161 x 161 DPI)



DOI: 10.1039/C4NR05194G

Nanoscale


Figure 7 The current-voltage characteristic of the organic active layer devices added with and without Au nanoparticles 0.20 mg/mL via different periods of time of ultrasonic vibration pretreatment. 110x80mm (169 x 169 DPI)



DOI: 10.1039/C4NR05194G

Page 27 of 29


Figure 8 The comparison between the absorption spectra of organic active layer devices added, respectively, with 0.10 mg/mL, 0.15mg/mL, 0.20 mg/mL, 0.30 mg/mL, 0.40mg/mL Au nanoparticles, and without, by ultrasonic vibration pretreatment for an hour. 119x84mm (214 x 214 DPI)



DOI: 10.1039/C4NR05194G

Nanoscale


Figure 9 The current-voltage characteristic of the organic solar cells with Au nanoparticles with the evaporation thickness of MoOx hole transport layer is in adjustment. 115x85mm (170 x 170 DPI)



DOI: 10.1039/C4NR05194G

Page 29 of 29


Figure 10

The external quantum efficiency of the organic solar cells with Au nanoparticles with the evaporation thickness of MoOx hole transport layer is in adjustment. 115x86mm (174 x 174 DPI)



DOI: 10.1039/C4NR05194G

nanoparticles.

Tailoring dispersion and aggregation of Au nanoparticles in the BHJ layer of polymer solar cells: plasmon effects versus electrical effects.

Plasmonic effect of spray-deposited Au nanoparticles on the performance of inverted organic solar cells.

Investigating the size effect of Au nanospheres on the photocatalytic activity of Au-modified ZnO nanorods.

grating-coupled surface plasmon enhanced photocurrent in TiO2 thin films.

Burstein-Moss Effect Behind Au Surface Plasmon Enhanced Intrinsic Emission of ZnO Microdisks.

Surface Plasmon Resonance Effect in Inverted Perovskite Solar Cells.

Enhancing the performance of polymer solar cells using CuPc nanocrystals as additives.

Transient Photocurrent Response of Plasmon-Enhanced Polymer Solar Cells with Gold Nanoparticles.

Surface engineering of ZnO nanostructures for semiconductor-sensitized solar cells.

Nanoscale mapping of plasmon and exciton in ZnO tetrapods coupled with Au nanoparticles.

Autocatalytic growth of ZnO nanorods from flat Au(111)-supported ZnO films.

Surface plasmon enhanced photoluminescence of ZnO nanorods by capping reduced graphene oxide sheets.

The effect of methanol treatment on the performance of polymer solar cells.

Enhanced infrared neural stimulation using localized surface plasmon resonance of gold nanorods.

Fabrication of Well-Aligned ZnO Nanorods Using a Composite Seed Layer of ZnO Nanoparticles and Chitosan Polymer.

Device performance of inverted polymer solar cells with AgSiO(2) nanoparticles in active layer.

The impact of surface chemistry on the performance of localized solar-driven evaporation system.

Study of the surface properties of ZnO nanocolumns used for thin-film solar cells.

Effect of aspect ratio and surface defects on the photocatalytic activity of ZnO nanorods.

A New Strategy for Silver Deposition on Au Nanoparticles with the Use of Peroxidase-Mimicking DNAzyme Monitored via a Localized Surface Plasmon Resonance Technique.

Effect of surface coating on the photocatalytic function of hybrid CdS-Au nanorods.

Efficiency Enhancement of Dye-Sensitized Solar Cells' Performance with ZnO Nanorods Grown by Low-Temperature Hydrothermal Reaction.

Hierarchically structured ZnO nanorods as an efficient photoanode for dye-sensitized solar cells.